Why Is Fawn Survival Plummeting?

Fawn recruitment is getting a lot of attention, more than at any other time in modern deer management history. Why? Because studies are showing huge declines in fawn survival. There has been a significant increase in the number of studies on fawn mortality and the reasons these studies are being done is the growing impacts of predators on fawns.

The big stimulus for this concern is coyotes, but it’s more than just coyotes. For the first time in the past 100 years, we have a myriad of predators in the eastern half of the United States. Black bear numbers continue to climb and they are spreading their range as well. Bobcat numbers are also up, and in some states are at an all-time high. An on-going study in northern Michigan noted bobcats took a surprising number of deer. Mountain lions have started to pop up in many Midwestern states. Although the previously mentioned predators all take some deer fawns, the major fawn predator is the coyote. A number of studies have shown coyotes eat fawns — and in some areas they eat a lot of fawns.

The most common method of study is to capture fawns, then put motion or temperature-sensitive radio collars on them. If the collar remains in one area for a certain period of time, or if the body temperature of the fawn drops rapidly, then the researchers rush in to check on the fawn.

In many present-day studies, when the fawn is found dead, DNA swabs are taken from the area of the body where predation occurred, and the researchers get a positive ID on what predator was involved. Neat bit of crime stopper stuff. So when you see a study on fawn mortality and there is a category listed as killed by “unknown predator,” you know DNA testing wasn’t done or unavailable when the study was done.

Back to the methods used in fawn mortality research. The approach of capturing a fawn and collaring showed, in general, fawn mortality from coyotes in the first 16 weeks of life was around 16 percent in the northern part of the country and 46 percent in the South.

For example, a North Carolina study showed only 5 of 27 collared fawns (18.5 percent) made it to 16 weeks. Fifteen of the 22 mortalities were caused by coyotes or bobcats and 55 percent of the mortality occurred the first week of life. (Note that most of these fawns were not captured on the day they were born and that is a critical factor. I’ll explain later).

Two Alabama studies showed a 33 and 31 percent fawn survival out to 16 weeks, which isn’t good. A Georgia study showed a 29 percent survival and a South Carolina study showed a 22 percent survival of fawns. Even worse.

An early 1990s study on the eastern shore of Maryland showed 91 percent survival of fawns from one week of age until the beginning of hunting season. In 2000 and 2001, Pennsylvania researchers captured and followed fawns until death in forested and in agriculture habitats. Of 110 fawns captured in farm country, 72 percent were alive after 9 weeks and 53 percent after 34 weeks. But things were a lot different in the forested habitat where 108 fawns were captured and 57 percent were alive after 9 weeks and 38 percent after 34 weeks. Because deer numbers were increasing in both habitats and over half the fawns survived out to 34 weeks, the researchers concluded that predation was not a major factor for deer survival in either habitat.

This past year, a Pennsylvania study showed a 52 percent survival out to 10 weeks. Of all the collared fawns killed, three were eaten by black bears, three by bobcats, one by a coyote, one by a dog, three from unknown predators (DNA results pending), five from natural mortality and one by car. Again, predation does not appear to be a major factor in Pennsylvania.

Now let’s back up and look at why the approach of capturing and collaring fawns might not give us the total picture relative to fawn predation. To collar the fawns, researchers search an area, find fawns bedded (or see them with their mothers), capture them and collar them. The problem with this approach is that most of the fawns are already one week old. Several recent studies show this approach might underestimate fawn predation.

These studies used a method that allowed fawns to be captured and collared at birth. Researchers did this by capturing adult does in the summer or fall and implanting a vaginal transmitter. When she gives birth to the fawn, she also gives birth to this implant and it signals the researchers to run in and mark the newborn fawn. With this approach, researchers discovered a lot of predation takes place that first week. In fact, the first week is the worst for fawn mortality from predators, especially coyotes. They concluded that all studies done with captured fawns that missed the first week underestimated the total fawn mortality due to coyotes.

What we now know is that getting that fawn through the first week of life is critical to its survival. One piece of the solution is an effective predator control program on your property.

This blog post is compiled of excerpts from a story originally posted on grandviewoutdoors.com. To read the original story by Dave Samuel at grandviewoutdoors.com click here.